Bioplastics derived from plant have become more important, because they can contribute various measures to oil depletion and global-warming. Further, because of concerns about future food shortages, it has become necessary to develop new bioplastics using a plant material of inedible parts.
As bioplastics utilizing inedible parts, plastics have been already developed and become commercial, in which an acid such as acetic acid and nitric acid or a petroleum-based modifier such as alcohol, for example, butyl alcohol is chemically bonded to cellulose, a primary constituent of inedible parts, and further a plasticizer and the like are added as required. For instance, Patent Document 1 discloses a thermoplastic biodegradable graft polymer, in which ε-caprolactone is grafted to cellulose acetate having a hydroxyl group through ring-opening polymerization.
However, since cellulose-based bioplastics are insufficient in mechanical properties such as strength, rigidity, toughness and the like, as compared to conventional petroleum-based plastics, utilization of cellulose-based bioplastics to durable products such as electronic equipment and automobiles has not yet proceeded. To expand utilization of cellulose-based bioplastics to these products, it is required to improve mechanical properties thereof further.
As means for improving mechanical properties of such bioplastics, a method is effective, in which a particulate, plate-like or fibrous filler is added, and farther a silane coupling agent or the like is used, thereby improving adhesion at an interface between the filler and a resin. In application to durable products, epoxy-based or amino-based silane coupling agents are effectively used together with, primarily, inorganic fillers, and have been used for many years. Further, a method of adding a nano-sized filler to form a nanocomposite is also effective, because the nano-sized filler has a feature that can substantially reduce the addition amount thereof, as compared to a normal-sized filler.
Meanwhile, the development of materials utilizing inedible part constituents other than cellulose has also been carried out. For instance, cardanol derived from cashew nut shells has been used for various purposes because of its excellent functionality owing to its distinctive molecular structure, in addition to stable production thereof.
As an example of the use of cardanol, Patent Document 2 discloses a friction material for brakes, which is formed using a fiber substrate comprising an aramid pulp and a cellulose fiber, filler comprising calcium carbonate and cashew dust, and a binder comprising a phenolic resin. Further, Patent Document 3 discloses a friction material formed using a base material comprising an aramid fiber and a cellulose fiber, a filler comprising graphite and cashew dust, and an organic/inorganic composite binder, and describes that this frictional material is used for clutch facing of drivelines for automobiles and the like.
Non-Patent Document 1 describes that water resistance of paper can be improved by performing a grafting reaction in which a paper sheet is dipped in cardanol to bond the cardanol to cellulose composing this paper sheet. It is described that in this grafting reaction, a terminal double bond of cardanol is bonded to a hydroxyl group of cellulose in the presence of boron trifluoride diethylether (BF3—OEt2).
Non-Patent Document 2 describes that tensile strength of a polyethylene resin is improved by bonding an isocyanate compound obtained by reacting cardanol with tolylene diisocyanate to a surface of sisal fiber.